Modal Auxiliaries for Probability:
1. Present/Future Probability
You will use may, might and could to represent events having a possibility to take place in the present and future.
- Suzan is in New York now. She may come tomorrow. (Future)
- Serena is not here. She might be outside. (Present)
- Don’t eat that old food, it was kept outside the refrigerator. It could be poisonous. (Present)
- Albert might go on a vacation this month. (Future)
- Alice has an exam today. She might be on the varsity now. (Present)
- Jeff has a meeting today. He may come tomorrow. (Future)
- Jack is not at the office. He might have a meeting outside. (Present)
- The movie is running very well. It may become a super hit. (Future)
You can use “might” because it is the best to represent probability. If you use “may”, it will be not so common and “could” is used in a positive sense.
- Most of the employees are absent today. The boss may not/ might not like this.
- Johnny may not/might not be a popular singer, but his voice is really good.
- Alice has an exam today. She may not/ might not attend the program.
- Alana is a calm and quiet person. She may not/ might not like the party.
2. Past Probability:
While representing positive probability about past you will use, may have/ might have/ could have and past participle form of the verb. While representing negative probability about past you will use may not have/might not have and past participle form of the verb.
- Serena is not in the city. She might have gone to her hometown. (Positive)
- Aric may have understood the math. The teacher taught him for a long time. (Positive)
- Lisa did not reply your message. She may not have seen it yet. (Negative)
- Jack did not do the assignment. He might not have understood the topic well. (Negative)
You have to be cautious that “could have” can only represent unreal conditions of the past.
- Lisa’s voice is really sweet. She could have won the contest if she had participated. (Positive)
- Suzan is a very good writer. She could have won the 1st prize if she participated in the easy contest.
You should also keep in mind that “couldn’t have” is only used to denote logically impossible thing in the past.
- Alana couldn’t have participated in the contest. She was hospitalized then.
- Aric couldn’t have sat for the exam. He was out of the city then.